Green roof systems are used on the roofs of buildings and provide an environment to host vegetation. A green roof system can offer energy consumption reduction, sound insulation, food and flower production, reduction of greenhouse gas emission, preservation of habitat and biodiversity, storm water retention, reduction in the urban heat island effect, and other benefits.
The main concerns for a green roof system include structural strength, managing or avoiding water leakage, and irrigation of roof plants. A building with a green roof must be strong enough to support the growth medium and the plants, especially after it is saturated with water. Waterproofing is a challenge as there may be a sustained water pressure on the roof in some systems. The aforementioned aspects are important for an intensive green roof, while irrigation is important for an extensive green roof. Current green roof technologies uses light weight growth medium to reduce the load on the infrastructure. For flat roofs, the main concerns are waterproof and structural design. For inclined roofs, the growth medium immobilization and water retention need extra considerations. Pitched sheets or stair-like designs have been used for this type of roof. The thinner growth medium layer of an extensive green roof allows less water uptake and retention. In areas with infrequent precipitation and/or high evaporation rates, irrigation may be required on a daily basis, which may offset the cost savings from a green roof system.
A similar situation requiring an environment to host vegetation exists in tree protection. Tree protection is important, especially for young and newly planted trees, whose root system has not yet well developed. Most widely used method is mulching with wood chips that are recycled from green waste. This can preserve moisture, reduce competition from weeds, and allow trees obtain essential nutrients to survive early growth. But they are not very efficient and long-lasting and will degrade quickly. Usually trees need to be re-mulched annually in spring.
One alternative solution for tree protection, especially for young trees, is to place weed mat around tree. These weed mats are usually made of plastic materials whose functions are just like mulch but last longer. Two different types of mats are available on the market right now: mats with and without pores. The major difference is that weed mat with pores allows rain water seep in while weed mat without pores cannot. It seems weed mat with pores are more effective for water permeate through; however, it is less favorable for the customers in the market. The argument preferring mat without pores is that the same pores that allow water seep in can quickly evaporate out because of its high surface area and small pore sizes. Both types of weed mats and wood chips' mulches rely primarily on the soil around trees for holding moisture. The mat or the mulch has no or very limited capability to absorb water. Therefore the moisture content can vary in a wide range depends on the properties of soil and weather.
Meanwhile, hundreds of billions of dirty diapers are disposed annually as solid wastes and only a very small fraction of them are recycled. This is mainly due to the lack of technologies for efficient and cost-effective recycling. The valuable materials in these disposed diapers could have found great applications if they can be properly processed.
Disposable diapers are made of a variety of components. First, an absorbent pad made of cellulose or cellulose acetate and superabsorbent polymer (SAP) e.g., sodium polyacrylate is used to absorb body fluids. This pad is then placed into a tissue carrier, which can be made of polyester nonwoven fabrics or tissue paper. This tissue wrapped pad is then sandwiched in between a layer of nonwoven fabric for interior and a non-permeable film for exterior. The nonwoven fabric includes of a hydrophilic layer to allow water to flow to the absorbent pad and a hydrophobic layer to keep the surface in contact with skin dry. The non-permeable film is made of polyethylene or cloth-like polyolefin films to prevent liquid leakage. To put all the above components together, hot-melt adhesives are used. Elastomeric materials, such polyurethane, polyester or rubber are used in cuffs for both the waist and the leg to maintain tightness. Adhesive tapes or hook tapes are used to provide mechanical grip for closure. Other components, such as lotions applied on the surface of top sheet, decorative film, wetness indicator, and acquisition and distribution layers are very common in disposable diapers.
The complexity of the disposable diapers arises from the consumers' need for a comfortable, effective, easy-to-use, and low-cost product. However, such a system has made traditional recycling impossible to do efficiently and cost-effectively with current technologies. As a result, most after-consumer disposable diapers end up as solid waste piling up in landfill fields. The lack of a product that can consume the recycled materials and proper purification technologies to produce high purity materials have played a great role in the landfill problem.